Super Insulation - Ideas?

[Christian Van H]

Originally Posted by Soundbounder

I am only speaking from my personal experience. I am sure there are products that have a better R-value.
Also, it only cost me a 12 pack of beer.

Sound, I agree. I'm just learnin' this stuff, and I guess I got spoiled looking at the R Value of those Vacuum panels. That Armaflex seems like a great idea for contours. Hey, your Blog is really, really beautiful! Its easy to tell that you truly love your subject! Thanks, Chris

[Cormorant]

We had an interesting experience last summer, wrapping a normally crappy old styrofoam cooler in one layer of Reflectix, the silver bubble-wrap style insulation that reflects infra-red radiation. You can buy it fairly cheap at home centers / lumber yards. That cooler went from a 2 day max for frozen food to 5 or 6 days. Makes me think that any icebox would benefit from similar treatment. The foam protects against conductive heat loss, and the Reflectix protects against radiative heat loss. Might be fun to try a foam-reflectix-foam-reflectix sandwich, or something like that.

[Christian Van H]

Hey Cormorant! Reflectix was already part of the plan. Great minds think alike! Wow, I didnt expect such a return for such a small investment. Thanks again, Chris

[Soundbounder]

Originally Posted by Christian Van H

Sound, I agree. I'm just learnin' this stuff, and I guess I got spoiled looking at the R Value of those Vacuum panels. That Armaflex seems like a great idea for contours. Hey, your Blog is really, really beautiful! Its easy to tell that you truly love your subject! Thanks, Chris

Thank you!!!!

[GordMay]

Originally Posted by Cormorant

We had an interesting experience last summer, wrapping a normally crappy old styrofoam cooler in one layer of Reflectix, the silver bubble-wrap style insulation that reflects infra-red radiation...

Radiant barriers* (reflective foil) like Reflectix must face an open dead air space, usually specified at a minimum of 3/4" to function properly.

As most boat refrigerators aren’t exposed to very much direct radiant energy (unlike a cooler in the sunlight), I would doubt the efficacy of installing a radiant barrier.

* A radiant barrier, as defined by the American Society of Testing and Materials (ASTM), is a reflective, low-emittance surface, that intercepts the flow of radiant energy to and from the building component.

Emissivity is the property that determines how well a radiant barrier will perform. This property is a number between 0 and 1, with lower numbers indicating better potential for performance. The emissivity of typical, clean, unperforated radiant barriers is about 0.03 to 0.05. Hence they will have a reflectivity of 95 to 97 percent. Some materials may have higher emissivities. It is not always possible to judge the emissivity just by visual appearance. Measured emissivity values should be part of the information provided by the manufacturer.

[LakeSuperior]

Gord,
Got to tell you here that you are off-base on the radiant barrier issue from several points of view. Cormorant is dead on here!

If you remove the air molecules (stop convection) between layers of radiation barriers you get vacuum insulation panels. The vacuum panels are some of the most efficient insulation (heat transfer resistance/unit thickness) on the planet.

Radiation barriers are designed to retard thermal radiative transfer at wavelengths of 2 to 50 micrometers which occurs in all directions. It is surprising to most people that the amount of thermal radiation (Watts/square dimension) incident on a surface is equivalent in magnitude to the solar radiation (radiation at ~0.3 to 2.0 micrometers wavelenth) which is directionally incident on a surface from a small area (the solar disk).

Consider that, if two homes in the winter have the same air temperature but only one is well insulated then a person will feel much more comfortable in the well insulated home. The home that is poorly insulated will feel cold because the cold walls are not radiating as much energy to the surface of your clothing.

The 3/4" air space rule is really arbitrary as radiation barriers work fine as long as there is not good thermal contact with an adjacent surface. This is especially true when the amount of heat transfer is small as is the case with refrigeration applications.

At the end of the day, the game is using material technologies to reduce conduction, convection, and radiation heat transfer to the desired level to allow the thinnest wall thickness thus maximizing the refrigeration volume.

[Christian Van H]

Jeez...I did'nt know I was startin' a battle of the Physicists!

[Stevens 47]

Originally Posted by Christian Van H

Hey Cormorant! Reflectix was already part of the plan. Great minds think alike! Wow, I didnt expect such a return for such a small investment. Thanks again, Chris

Christian,

Just curious on what you decided. This is a upcoming project, I would love to get the low down on your material choices and construction methodology.

[GordMay]

Heat transfer occurs whenever there is a temperature difference between two bodies. It can occur through one or more different mechanisms; conduction, convection, and radiation.

Conduction requires an intimate contact between two solids.

Convection also requires contact with a liquid or gas.

Radiation heat transfer, on the other hand, may occur across any open space, including vacuum. Thermal radiation is electromagnetic radiation emitted by the atoms and molecules. Reflective materials include radiant barriers and reflective insulations.

A radiant barrier is a single sheet of reflective materials positioned on one side of a cavity. The radiant barrier itself provides no significant thermal resistance; it must be installed in conjunction with an air space.

Reflective insulation is a system of reflective sheets and air spaces designed together to fill a cavity and act as insulation. Thus, reflective insulation would consist of a number of layers of air spaces and reflective sheets.

Some advertisements for radiant barriers show the material acting as a shield against the heat radiating from sun lamps. This introduces the point that if the principal mechanism of heat transfer is radiation, then a reflective system will reduce heat transfer. This has been recognized in window technology; high-thermal-performance windows are designed to reduce radiation, because two-thirds of the heat loss through windows occurs by radiation.

Conversely, if the primary mechanisms of heat loss through the envelope are conductive or convective, then addressing radiation alone will not be adequate.

Since reflective films are foils, they act as vapour barriers and, as such, should not be installed on the cold side of a cavity without precaution, e.g., adequate perforation.

In general, multiple reflective materials do not address conduction and convection losses in envelope cavities well enough to warrant their use in refrigeration. Additional work to improve these products may make them more effective and ensure that they do not adversely affect thermal performance or envelope durability.

In terms of cost, reflective materials are subject to the same principles of diminishing returns as conventional insulation. If it is not cost-effective to add more conventional insulation, it is probably not cost-effective to add a radiant barrier.

[Christian Van H]

Originally Posted by Stevens 47

Christian,

Just curious on what you decided. This is a upcoming project, I would love to get the low down on your material choices and construction methodology.

Hey Stevens! Nothing is final yet, and my design is relatively radical. As it stands, I have designed a fridge/freezer using a A/B Super ColdMachine with one holding plate. This is where it gets strange. Both Freezer and fridge compartments are drawers. The holding plate mounts up under the divider between the freezer below and the above fridge. A temp controlled fan circulates air captured on the backside of the plate up into the fridge compartment. Right now the plan is for 6 to 8 inches of reg. hard closed cell foam insulation around the liner, wrapped in reflectix, with a 1 inch air gap around that. Drawer fronts are insulated with two layers of vacuum panels, with a stepped seal arrangement. Originally a front opening box, the drawers will hold some of the cold air from escaping when opened, while holding in all of the contents when heeled. Thats it so far...

[bobfnbw]

Very interesting subject to us as well.
The stock fridge on our 23 year old Endeavour will be redone at some point, as well as the freezer in the walk thu. Currently there is about 2-3 inches at best with a fibeerglass liner. The super cold machine does a resonable job, but I feel of course that something else would be better in the longer term.

In searching for materials to build the box, it seems that isocyanurate foam, sprayed in, with 3-4 inches for refrig and 6 inches for freezer space would be ideal, but I am not sure that that is a do it yourself project.
Also mcmaster-carr sells Polyurethane Foam sheets at 2- 4" thick that would do as well.
Vacuume panels while having potentialy large r values, are pricy, and can be punctured thereby losing most of your r value. I think I will stay with the foam, and build my own box, has to be a lot better than what is presently onboard.

[Cheechako]

I spent the time to put the vacuum panels in my Passport. Frankly, I didnt see any positive effect afterward. However, I changed to a 1/2hp belt drive unit at the same time because I read too many books and articles. That unit sucked amps like a black hole!

[chala]

In a super maramu passing through darwin, the people on board show me some insulation that they bought in NZ, they recon it was fabulous, apparently it is used in clothing looks like little threads, possible name thinsulate 3M, checked 3m supplier in Australia apparently we are not cold enough and did not import. I could not find the Resistivity value.

[Soundbounder]

Originally Posted by chala

In a super maramu passing through darwin, the people on board show me some insulation that they bought in NZ, they recon it was fabulous, apparently it is used in clothing looks like little threads, possible name thinsulate 3M, checked 3m supplier in Australia apparently we are not cold enough and did not import. I could not find the Resistivity value.

You are right, it is a 3M product.
Here is a photo of it:
Google Image Result for http://www.pennineoutdoor.co.uk/prods/large/thinsulate.jpg
It looks like you would need to encapsulate it, or cover it with some sort of barrier wrap.

[chala]

They had it wraped in a sort of water proof cloth in batten 10mm thick by 100mm wide, was easy to do they said, did the job them self. For curiosity Soundbounder are you able to find the R value in metric? just to compare with other product.